We have investigated the temperature dependence of threshold voltage (Vth) ofn‐channel GaAs metal–semiconductor field effect transistors with different gate materials and structures. It is found thatVthincreases by 0.3–0.4 V as temperature decreases from 350 to 80 K. TheVthversus temperature relationship is approximately linear. The amount ofVthshift is independent of channel length from 0.8 to 3 μm and it does not strongly depend on the gate material used. SimilarVthincreases are observed for different channel doping methods, such as ion implantation and molecular‐beam epitaxy growth. Different GaAs substrates only show a small effect on theVthtemperature dependence. Calculations show that Fermi‐level shift and energy‐gap expansion with decreasing temperature account for only a fraction of the observed change inVth. Our measurements indicate that the extraVthshift is not mainly due to deep‐level traps within the channel. Results fromC–Vmeasurements on metal/GaAs diodes suggest that build‐in voltage changes with temperature are principally responsible for theVthshift.